At the present day, an unsaturated nitrile which is generally available commercially is mainly produced industrially by the catalytic ammoxidation reaction of olefin, ammonia, and oxygen. On the other hand, in recent years, a method for subjecting an alkane such as propane or isobutane as a raw material in place of the olefin to a vapor-phase catalytic ammoxidation reaction to produce a corresponding unsaturated nitrile has attracted people's attention. Various catalysts used in the case have also been proposed.
Patent Literature 1 describes a catalyst wherein a composite metal oxide containing Mo, V, Nb, and B is supported by 20 to 60% by mass of silica in terms of SiO2 based on the total mass of an oxide and silica, as a catalyst for the vapor-phase catalytic oxidation or vapor phase catalytic ammoxidation of propane or isobutane.
Patent Literature 2 describes a silica-supported catalyst used when propane or isobutane is subjected to a vapor-phase catalytic ammoxidation reaction to produce an unsaturated nitrile, or the propane or isobutane is subjected to a vapor-phase catalytic oxidation reaction to produce an unsaturated carboxylic acid, wherein the silica-supported catalyst has a specific metal component composition, a silica content rate, and a pore volume.
Generally, when focus is on the ratio of V/Sb in an MoVSbOx type ammoxidation catalyst, V is more than Sb. Such a ratio has been well known in an ammoxidation catalyst synthesized by hydrothermal synthesis or the like (for example, see Non Patent Literature 1). Therefore, also in an MoV type ammoxidation composite oxide catalyst prepared by a method except the hydrothermal synthesis, the amount of V to Sb has been adjusted so as not to decrease the amount if possible or so as to increase the amount.
Patent Literatures 3 shows a catalyst having an improved reaction yield and catalyst life. However, a large amount of V is still used. On the other hand, in the actual reaction, it has been known that Mo in an active structure forms a complex with water generated by a catalytic reaction or a side reaction, which causes the escaping of Mo. In the case of an MoV composite crystal, the escaping of Mo relatively increases V in the composite crystal to excessively increase the activity to the raw material.